Light-stable colored transparent composite films

ABSTRACT

Composite film structures exhibit a predetermined finished color tone comprised of a transparent film layer which exhibits a color deficiency as compared to the finished color tone, and a pigment which is visually associated with, and satisfies the color deficiency of, the film layer. Most preferably, the pigment is provided as a homogenous dispersion in a transparent color-matching layer positioned adjacent to the film layer. Thus, when the film and color-matching layers are viewed collectively as a unit, the perceived color tone will be that of the finished predetermined color tone. That is, the color-matching layer provides visually an additive effect on the perceived color of the composite film structure.

FIELD OF THE INVENTION

The present invention relates to colored transparent films. Inparticularly preferred forms, the present invention is embodied incolored transparent composite films which exhibit exceptional lightstability (anti-fading) characteristics.

BACKGROUND AND SUMMARY OF THE INVENTION

Transparent colored films are employed in a number of end-useapplications, for example, as window films, light filters and the like.When employed as window films in the building and automotive industries,the colored transparent window films are typically adhered to glasswindow surfaces via a suitable adhesive so as to reduce the amount ofnear infra-red, ultra-violet and/or visible radiation entering thebuilding or automotive interior space. Such solar films therefore assistthe occupants by providing less glare, reducing interior heating effectsand the like.

Colored transparent films are typically provided by dyeing a suitablethermoplastic (preferably polyester) film substrate as is disclosed morecompletely in U.S. Pat. Nos. 3,989,453; 3,943,105; 3,932,126; 4,050,892and 4,047,889 (the entire content of each being incorporated expresslyhereinto by reference). Thus, the thermoplastic film substrate may bepreconditioned to enhance affinity to solvent or disperse dyes, followedby contacting the preconditioned film substrate with an organicdye-containing paste or solution.

Gray-toned (i.e., so-called “smoke-colored”) transparent films areespecially desirable in the market and are produced by suitable dyeingof the film substrates using the necessary proportions of red, blue andyellow organic dyes. One problem which these conventional gray-tonedtransparent films experience, however, is that the yellow dye componentis more susceptible to light degradation as compared to the red and bluedye components. Thus, over prolonged exposure to light, the yellow dyecomponent of the gray-toned dyed film tends to decompose (fade) therebychanging the visual appearance of the film undesirably to a more purplecolor tone due to the then more dominant presence of the red and bluedyes remaining in the dyed film.

It would therefore be especially desirable if colored (dyed) transparentthermoplastic films could be rendered more light stable therebyminimizing (or preventing entirely) fading and/or changing color tonesover time. It is towards fulfilling such a need that the presentinvention is directed.

Broadly, the present invention is embodied in composite film structuresexhibiting a predetermined finished color tone comprised of atransparent film layer which exhibits a color deficiency as compared tothe finished color tone, and a pigment which is visually associatedwith, and satisfies the color deficiency of, the film layer. Mostpreferably, the pigment is provided as a homogenous dispersion in atransparent color-matching layer positioned adjacent to the film layer.Thus, when the film and color-matching layers are viewed collectively asa unit, the perceived color tone will be that of the finishedpredetermined color tone. In other words, the color-matching layerprovides visually an additive effect on the perceived color of thecomposite film structure.

As a practical matter, therefore, the color deficiency of the film layercan be selected to be that particular dye which is more light unstableand thereby more likely to degrade over time when exposed to light. Thepigment in the color-matching layer (which would inherently be morecolor stable as compared to the dye) may then be selected to satisfy thecolor deficiency in the film layer. As a result, a more light stabletransparent color film composite structure ensues (i.e., due to thelesser amount (if any) of more light unstable dye(s) in the film and thegreater amount of more light stable pigments in the adjacentcolor-matching layer).

These and other aspects and advantages of the present invention willbecome more clear after careful consideration is given to the followingdetailed description of the preferred exemplary embodiments.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS

The file of this patent contains at least one drawing executed in color.Copies of this patent with color drawing(s) will be provided by thePatent and Trademark Office upon request and payment of the necessaryfee.

Reference will hereinafter be made to the accompanying drawings, whereinlike reference numerals throughout the various FIGURES denote likeelements, and wherein,

FIG. 1 is a greatly enlarged schematic cross-section of one embodimentof a composite film in accordance with the present invention;

FIG. 2 is a greatly enlarged schematic cross-section of the compositefilm depicted in FIG. 1 applied onto a glass substrate;

FIG. 3 is a greatly enlarged schematic cross-section of anotherembodiment of a composite film in accordance with the present invention;

FIG. 4 is a greatly enlarged schematic cross-section of yet anotherembodiment of a composite film in accordance with the present invention;

FIGS. 5-9 are graphical representations of the color stability test dataobtained by the Example 2 below; and

FIGS. 10-13 are color photoprints each visually depicting thenon-weathered finished color tone (visible on left-hand side of eachsample) and the results of accelerated weather testing (visible on theright-hand side of each sample) on such finished color tone obtainedaccording to Example 2 below, wherein FIG. 10 is a sample in accordancewith the present invention, and FIGS. 11-13 are each representative ofcommercially available transparent colored films.

DETAILED DESCRIPTION OF THE INVENTION

I. Definitions

The terms “hue”, “chroma” (sometimes referred to in the art as intensityof color saturation) and “value” are the color coordinates associatedwith the Munsell color system (see U.S. Pat. No. 824,374, the entirecontent of which is incorporated fully hereinto by reference).

The term “colorant” is any material which exhibits hue, chroma and/orvalue. Thus, a colorant may be one which exhibits a perceived color(e.g. red, blue and/or yellow) in which case it has a definite hueand/or chroma and is characterized as being chromatic. A colorant mayalso be a material which lacks both hue and chroma, but whichnonetheless contributes to the value coordinate, in which case it ischaracterized as achromatic.

A ‘pigment’ is a particulate material which is a colorant.

The term “transparent” connotes the ability to perceive visually anobject, indicia, words and the like through a medium, which is a film inthe preferred embodiment of this invention. More specifically, the term“transparent” as used herein and in the accompanying claims means themedium (e.g., film) exhibits a haze value (ASTM D 1003-61) of notgreater than about 25%, preferably not greater than about 5%, and avisible light transmission (VLT) through the film structure (ASTM E903and NFRC 300-93. “Procedure for Determining the Solar Optical Propertiesfor Simple Fenestration Products”) of between about 1% to about 90%,preferably between about 5% to about 80%, and most preferably betweenabout 5% to about 50%. The particular haze value and VLT of a filmstructure will thus depend on its intended end use application. Forexample, window films for use with automotive glass will typically havea relatively low have value (e.g., not greater than 5%) and a relativelyhigh VLT (e.g., between about 5 to about 50%). Film structures intendedfor shade applications, however, can tolerate relatively greater hazevalues and relatively lower VLT as compared to automotive window films.

II. Detailed Description of the Preferred Embodiments

Accompanying FIG. 1 shows an enlarged schematic cross-section of oneembodiment of a composite film 10 having a finished color tone inaccordance with the present invention. Specifically, the composite film10 necessarily includes a film layer 12 and a color-matching layer 14.The film layer 12 is formed of a suitable thermoplastic, preferably apolyester, such as polyethylene terephthalate (PET), or other suitablethermoplastics, such as, for example, polyacrylic, poiyimides,polyamides (e.g., nylons), and polyolefins (e.g., polypropylenes,polyethylenes and the like). The thermoplastic films employed in thepractice of this invention can include conventional additives eithercoated upon, or homogeneously blended within, the film. Thus, thethermoplastic films may include UV-absorbers, stabilizers, fillers,lubricants and other processing aids, and the like.

The thickness of film layer 12 is most advantageously between about 0.25mil to 14 mils. For example, when composite film 10 is employed as asolar film for windows, the thickness of film layer 12 is typically inthe range between about 0.5 to about 1.0 ml. When the composite film 10is employed for other applications, such as a sun shade, the thicknessof film layer 12 may be between about 1.0 mil to about 3.0 mils.

The film layer 12 may be uncolored or colored. If uncolored, then thefilm layer 12 will exhibit a complete deficiency in all three colorcoordinates of hue, chroma and value. If colored, then the film layer 12will exhibit a deficiency in a least one color coordinate of hue, chromaand value as compared to the finished color tone of the composite film10. In either the uncolored or colored case, therefore, the film layer12 will exhibit a deficiency in at least one of hue, chroma and value ascompared to the finished color tone of the composite film 10.

The color deficiency of the film layer 12 is satisfied in thecolor-matching layer 14. Specifically, the color matching layer 14includes a homogeneous dispersion of pigment therein which satisfies thecolor deficiency in the film layer 12. As a result, when the film andcolor-matching layers 12, 14 are viewed collectively, the additiveeffect of their respective color tones will result in a visualperception corresponding to the finished color tone of the compositefilm 10. Most preferably, the color-matching layer is interior of thefilm layer 12 (i.e., positioned closer to the sunlight than the filmlayer 12).

In the composite film 10 shown in FIG. 1, the color-matching layer 14 ismost preferably formed by dispersing the pigment throughout a mountingadhesive. Virtually any suitable pressure or non-pressure sensitivemounting adhesive may be employed in the practice of the presentinvention which allows the composite film 10 to be adhered securely to adesired support substrate. In this regard, the preferred mountingadhesive is an acrylic pressure sensitive adhesive commerciallyavailable from Solutia, Inc. under the tradename GELVA® 263 adhesivewhich is supplied as an acrylic resin solution.

The pigment that is employed in the practice of the present invention isbroadly characterized as a particulate colorant material. That is, thepigment will impart a desired color tone to the color-matching layer andis selected based on its color characteristics of hue, chroma and/orvalue as well as its average particle size properties. Thus, the pigmentemployed in the present invention can be either chromatic in that is hasat least one of hue and chroma characteristics, or can be achromatic inwhich case it is lacking in both hue and chroma characteristics but hasa value characteristic. The pigment also cannot have too large aparticle size as this would adversely scatter light making the compositefilm less transparent (i.e., more hazy, translucent or opaque).Therefore, the pigment employed in the practice of the present inventionis required to have an average particle size of less than about 0.50 μm,more preferably less than about 0.10 μm, and most preferably less thanabout 0.05 μm.

Virtually any pigment that satisfies the above-noted criteria may beemployed in the practice of this invention. Thus, pigments based on ironoxide, lead, chrome, ultramarine, iron blue, cadmium and the like may beemployed. For example, when the color deficiency in the film layer 12 iswith respect to the yellow hue and/or chroma, then a particularlypreferred pigment is red iron oxide (which actually visibly has ayellowish color tone).

When employed as a dispersion within the mounting adhesive, the pigmentsemployed in the practice of the present invention may conveniently bemixed with the adhesive so as to be homogeneously dispersed therein andthen applied onto the film layer 12 as the color-matching layer 14 inany known manner, such as dipping, spraying, padding, roller coating,gravure coating, printing or the like. Following application, thecolor-matching layer 14 (i.e. the adhesive material containing ahomogenous dispersion of pigment therein) may be covered by a suitablerelease layer 18 to allow the composite film 10 to be handled andshipped prior to being mounted onto a substrate. In this regard, justprior to use, the release layer 18 will be removed or peeled away fromthe adhesive (color-matching) layer 14 thereby leaving the remaininglaminated components of the composite film (noted by reference numeral10′ in FIG. 2). The composite film components 10′ may then be affixed toa substrate, for example, a glass substrate (e.g., a building orautomotive window) 20 as shown in FIG. 2.

One particularly preferred embodiment of the present invention is agray-toned composite film having a film layer 12 which is colored withpredominantly red and blue dyes and thus will exhibit a yellow colordeficiency (i.e., will exhibit a purple-like color tone). Thus, thepreferred gray-toned composite may be dyed with a minor, butinsufficient, amount (if any) of a yellow dye. The color-matching layer14 will thus be formed of a mounting adhesive in which a yellow coloredpigment (e.g. an iron oxide) is dispersed homogeneously. Thus, theyellow-colored pigment in the color-matching layer 14 will satisfy theyellow color deficiency of the dyed film layer 12.

The composite film 10 may also include an exterior (i.e., relative tothe rigid substrate, typically glass, on which the film is adhered)polymeric protective coating 16 (typically called a “hardcoat” in artparlance). The protective coating 16 serves to impart abrasionresistance, scratch and/or chemical resistance to the composite film 10or 10′. Typically, such coatings are curable either thermally or byradiation and can be, for example, highly cross-linked acrylic acidesters. Particularly preferred materials that may be employed in theprotective coating 16 are the radiation polymerizable acrylic coatingsdisclosed more fully in U.S. Pat. No. 4,557,980 (the entire content ofwhich is expressly incorporated hereinto by reference). If present, theprotective coating 16 will typically have a thickness of less than 10μ,and preferably between about 1μ to about 4.5μ.

Although the composite film 10 has been described wherein the pigment isdispersed throughout an adhesive material so as to form thecolor-matching layer 14, it may be desirable to disperse some (or all)of the pigment in the protective coating 16, in which case both thelayers 14 and 16 (or just the layer 16) constitute the color-matchinglayer to satisfy the color deficiency of the film layer 12. Furthermore,it is possible that the pigment could be dispersed throughout, and thusbe integrally provided with, the film layer 12. The film layer 12 withits integral dispersion of pigment could then be dyed to have a colordeficiency which is integrally satisfied by the pigment containedtherewithin.

Accompanying FIG. 3 shows another embodiment of a composite film 30according to the present invention. In this regard, like the compositefilm 10 discussed above, the composite film 30 includes a thermoplastic(preferably PET) film layer 12, a color-matching adhesive layer 14containing a pigment dispersed therein, a protective exterior coating16, and a release layer 18 covering the adhesive color-matching layer14. However, according to the embodiment depicted in FIG. 3, thecomposite film 30 is provided with another film layer 32 which isadhered to the film layer 12 by a suitable laminating adhesive layer 34.

The film layer 32, like the film layer 12 may be uncolored or colored asmay be desired. Furthermore, the film layer 32 may be metallized. Thatis, the film layer 32 may be provided with a relatively thin metalcoating, e.g., aluminum, nickel alloys (e.g., nickel-chromium alloys ortheir oxides), silver, titanium and the like, applied by conventionalvacuum deposition techniques. If present, the metallized layer willtypically have a thickness of between about 50 Å to about 600 Å.

The pigment in the adhesive color-matching layer 14 may alternatively,or additionally, be provided in the laminating adhesive layer 34, ifdesired. Thus, the pigment may be distributed among the layers 16, 14and 32, or be contained in any one of such layers as may be desired. Forexample, as shown in FIG. 4, a laminated composite film 40 is providedwith thermoplastic film layers 42 and 44 laminated to one another with asuitable adhesive layer 46. One or both of the film layers 42, 44 maythus be dyed in a manner which provides for a color deficiency ascompared to the finished color tone of the composite film 40. A pigmentsatisfying the criteria noted previously may thus be dispersedhomogeneously throughout the adhesive layer 46 so as to satisfy thecolor deficiency of the film layers 42 and/or 44. The composite film 40depicted in FIG. 4 is thus suitable as a window shade film.

The transparent films according to the present invention can be“engineered” to provide desired light transmission characteristics,depending on the end-use application. Most preferably, the coloredtransparent composite films will have a visible light transmission (VLT)of between about 1% to about 90%, preferably between about 5% to about80%, and most preferably between about 5% to about 50%. The transparentfilms of this invention will also most preferably exhibit haze values ofnot greater than about 25%, preferably not greater than about

III. EXAMPLES

The present invention will be further understood after consideration isgiven to the following non-limiting Examples.

Example 1

A red iron oxide (Cl R101) pigment was blended with a scratch-resistantmethyl methacrylate hardcoat material (U.S. Pat. No. 4,557,980) usingmethyl iso-butyl ketone (MIBK) solvent in an amount of 1 wt. % ironoxide in the hardcoat plus MIBK. The resulting mixture had CIE labvalues (10° standard observer and D65 light source) ofL*=94.18/a*=0.84/b*=9.25 and was applied at a thickness of 1.0-1.5microns using standard gravure coating methods onto a dyed polyesterfilm so as to achieve a gray color tone. CIE Lab values (100 observerwith 065 light source) for the resulting coated film were:L*=81.13/a*=−3.96/b*=−4.9. The coated film was mounted on clear, singlestrength glass using an acrylic pressure sensitive adhesive (GELVA® 263adhesive, Solutia, Inc.) which contained a benzophenone UV-absorber. Thefilm and glass structure was then subjected to accelerated Xenon weathertesting according to ASTM G26-93. The film showed enhanced colorstability characteristics after 1200 hours exposure to the Xenon weathertesting conditions.

Example 2

A red iron oxide (Cl R101) pigment was blended in an amount of 1 wt. %with an acrylic pressure sensitive adhesive (GELVA® 263 adhesive,Solutia, Inc.) which contained a benzophenone UV-absorber. The resultingblend of red iron oxide pigment and adhesive was used to mount the samedyed gray-tone polyester film employed In Example 1 to a clear, singlestrength glass for weather testing according to ASTM G26-93.

The results of the weather testing on the composite film in accordancewith the present invention were compared to the weather testing resultsof three dyed polyester film products commercially available fromCPFilms, Inc. of Martinsville. VA, identified by AT 35 Gr SR HPR (Comp.1), AT 35 Ch SR HPR (Comp 2) and AT 35 Bz SR PS (Comp 3). The results ofsuch comparative testing are shown graphically in the accompanying FIGS.5-9. In addition, the results of the accelerated weather testing areshown photographically in accompanying FIGS. 10-13. In this regard, theleft-hand side of each of FIGS. 10-13 represents the finished color toneof the film unexposed to the weather testing conditions, whereas theright-hand side of FIGS. 10-13 was exposed to, and thus depict thecondition of the film after, weather testing. As is evident, thecomposite film in accordance with the invention (FIG. 10) shows enhancedcolor stability characteristics as compared to the conventional filmsComp. 1 (FIG. 11), Comp. 2 (FIG. 12) and Comp. 3 (FIG. 13).

Example 3

Example 2 was repeated except that the 1 wt. % iron oxide containingadhesive was used to laminate a metallized film (1 mil thick aluminummetallized layer on a 15% visible light transmission gray-toned dyedpolyester film) toga 0.5 mil thick clear polyester film containing UVabsorbers. The resulting laminated composite film structure was mountedto a single strength glass using a non-pigmented acrylic pressuresensitive adhesive (GELVA® 263 adhesive, Solutia, Inc.) which containeda benzophenone UV-absorber. Following weather testing, the sample wasvisually observed for corrosion and coating instability with nosignificant anomalies being detected.

While the invention has been described in connection with what ispresently considered to be the most practical and preferred embodiment,it is to be understood that the invention is not to be limited to thedisclosed embodiment, but on the contrary, is intended to cover variousmodifications and equivalent arrangements included within the spirit andscope of the appended claims.

1-34. (canceled)
 35. A transparent film which exhibits a predetermined finished color tone comprising: a color-deficient, dyed, polymer film layer which exhibits a color deficiency in at least one of hue, chroma, and value as compared to said predetermined finished color tone; and, a pigment having an average particle size of less than about 0.50 microns which is visually associated with said polymer film layer, wherein said pigment exhibits a matching color tone satisfying said color deficiency of said polymer film layer to thereby impart to said transparent film said predetermined finished color tone when said polymer film layer and said pigment are viewed collectively as a unit.
 36. The transparent film of claim 35, wherein said pigment is dispersed throughout said transparent film.
 37. The transparent film of claim 36, wherein said pigment comprises iron oxide, lead, chrome, ultramarine, iron blue, or cadmium.
 38. The transparent film of claim 36, wherein said at least one pigment has an average particle size of less than about 0.10 microns.
 39. The transparent film of claim 36, wherein said at least one pigment has an average particle size of less than about 0.05 microns.
 40. The transparent film of claim 36, wherein said polymer film layer comprises a polymer selected from the group consisting of poly(ethylene terephthalate), polyacrylic, polyimide, polyamide, and polyolefin.
 41. The transparent film of claim 36, wherein said polymer film layer comprises poly(ethylene terephthalate).
 42. The transparent film of claim 36, wherein said transparent film has a thickness of 0.25 mils to 14 mils.
 43. The transparent film of claim 36, wherein said transparent film has a thickness of 0.5 mils to 1.0 mils.
 44. The transparent film of claim 36, wherein said transparent film has a thickness of 1.0 mils to 3.0 mils.
 45. The transparent film of claim 36, wherein said transparent film further comprises an adhesive layer adjacent said polymer film layer.
 46. The transparent film of claim 45, wherein said adhesive layer comprises an acrylic pressure sensitive adhesive.
 47. The transparent film of claim 45, wherein said adhesive layer comprises a pigment having an average particle size of less than about 0.50 microns.
 48. The transparent film of claim 47, wherein said adhesive layer comprises a pigment that is different than said pigment in said polymer film layer.
 49. The transparent film of claim 36, wherein said transparent film further comprises a hardcoat adjacent said polymer film layer.
 50. The transparent film of claim 36, wherein said transparent film further comprises a metallized layer on said polymer film layer.
 51. The transparent film of claim 35, wherein said transparent film further comprises an additional layer laminated to said polymer film layer
 52. The transparent film of claim 36, wherein said transparent film further comprises an additional layer laminated to said polymer film layer
 53. A layer of glass having disposed thereon a transparent film which exhibits a predetermined finished color tone, wherein said transparent film comprises: a color-deficient, dyed, polymer film layer which exhibits a color deficiency in at least one of hue, chroma, and value as compared to said predetermined finished color tone; and, a pigment having an average particle size of less than about 0.50 microns which is visually associated with said polymer film layer, wherein said pigment exhibits a matching color tone satisfying said color deficiency of said polymer film layer to thereby impart to said transparent film said predetermined finished color tone when said polymer film layer and said pigment are viewed collectively as a unit. 